Vesta rock turns for Dawn probe

More of asteroid Vesta's southern polar region, seen from a distance of about 10,500km

The giant asteroid Vesta is revealing more of itself to the US space agency's (Nasa) Dawn mission.

The probe has beamed back further images since entering into orbit around the 530km-wide rock on 17 July.

Dawn took the latest batch as it was travelling from the day side to the night side of Vesta.

The different lighting conditions provide scientists with additional information about the varied features on the rock's pockmarked surface.

As Dawn circles its target, so the asteroid itself turn on its axis. The rock rotates once every five hours and 20 minutes.

Dawn will spend a year studying Vesta before moving on to the biggest object in the asteroid belt between Mars and Jupiter - the dwarf planet Ceres.

Already, though, there is much to excite those interested in the Solar System's minor planetary bodies.

Dawn's principal investigator says he has been surprised by the number and size of the impact craters on Vesta - there are far more of them and they are much bigger than he had expected before the mission set out.

And in a tantalising trailer of pictures yet to be released, Professor Chris Russell, from the University of California Los Angeles told the BBC this week: "The surface is much more colourful; the colours are deeper than they are on the [Earth's] Moon.

"The Moon is rather bland compared to the surface [of Vesta].

"That was my first surprise when we started taking some colour images. There are orange regions, and bluish regions. The colours are deeper than I've seen before on asteroidal and lunar-type bodies."

We should start to see some of these colour pictures in the next week or so.

Asteroids are fascinating for what they can tell us about the earliest days of the Solar System.

These wandering rocks are often described as the rubble that was left over after the planets proper had formed.

Vesta and the 950km-wide Ceres are both evolved bodies - that is, objects that heated up and started to separate into distinct layers.

In the case of Vesta, this process became quite advanced. It probably has a metal core and scientists expect to see evidence on its surface of past high temperatures, and perhaps even ancient lava flows.

Ceres on the other hand is much less dense, indicating it retains large quantities of water. Scientists suspect this could be in an icy band hidden below a dusty surface.

The images we have seen so far of Vesta have come from Dawn's framing camera system, which was developed and built under the leadership of the Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany.

This image was acquired last weekend. Here the distance to Vesta is about 15,000km